I'm not going to be all high and mighty then say that tests should have caught this since Apache has tests. I am not sure why RewriteCond expr is even valid at all since expr typically needs an expression to come after it like RewriteCond expr "'cache/%{md5:%{REQUEST_URI}?%{QUERY_STRING}}.html' =~ /(.+)/".

The bug appeared to be introduced on July 7 with a backport from trunk:

https://github.com/apache/httpd/blame/ed99ef021de902363c36af...

It took me a second but the fix addresses the case where rc==0. If statement is less than 0. Therefore, rc==0 should indicate no match. https://github.com/apache/httpd/commit/8abb3d06b23975705ebcf...

I suppose because there is also the conditional for err?